Hybrid component with high strength/mass ratio and method of manufacturing said component

ABSTRACT

The invention provides a high-strength hybrid component comprising a relatively soft first part -made of a composite material consisting of an organic matrix reinforced with fibres, a relatively hard second part made of metal, metal alloy or ceramic, and a transition layer made of a composite material consisting of a matrix of a material which is weldable to the hard part and fibres which are extensions of the fibres of the soft part. The transition layer matrix and the hard part may be formed by deposition of molten material on to the fibre preform of the soft part, using flame, electric arc or plasma, and the resin matrix of the soft part is impregnated into the preform and polymerized afterwards. 
     Alternatively, the hard part may be machined to shape and welded to the transition layer before completing the soft part.

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to hybrid components which comprise at least onefirst part made of composite material consisting of a fibre-reinforcedorganic resin matrix, and at least one second part added to it and madeof metal, metal alloy or ceramic material. Examples of such componentsmay include, inter alia, a link with an added head, a turbomachine bladewith an added leading edge, and a casing with added bosses.

The invention also relates to a method of manufacturing such components.

2. Summary of the prior art

Components made of composite material comprising a mass of reinforcementfibres, for example of carbon or silicon carbide (SiC), embedded in amatrix of polymerization-hardened organic resin are often used inindustry, particularly in the aeronautics industry, on account of theirhigh strength/mass ratio compared with similar components made entirelyof metal. In the components with the best performance, the reinforcingfibres are made into preforms before their impregnation with resin. Apreform is an assembly of sheets of fabric which are woven from thefibres intended to form the reinforcement, the sheets of fabric beingcut out and assembled together to form at least partly the shape of thecomponent to be made, and thus take up at least part of its volume. Thepreform may also be made as a monofabric, i.e. a fabric constituted byseveral sheets of fibres woven together, such a fabric exhibiting aparticularly high resistance to decohesion between the sheets of fibres.However, such components made of composite material pose difficultiesresulting from the general properties of the organic resin constitutingthe matrix, namely low hardness and low resistance to temperature, suchdifficulties not occurring with metal or ceramic components.

A first problem is, therefore, to make components of composite materialhaving a fibre-reinforced organic matrix, in which the parts which arestressed and able to assume a great variety of shapes will be made ofmetal, metal alloy or ceramic capable of taking the stress and formed tothe required shape.

The difficulty lies in the method of bonding between the organiccomposite part and the metal part, when the area of contact betweenthese two parts is subjected to concentrations of stresses:

of mechanical origin when the metal part protrudes from the compositepart and is subjected to stresses tending to pull it out;

of mechanical origin, again, as a consequence of different moduli ofelasticity or Young's moduli;

of thermal origin, as a consequence of very different thermal expansioncoefficients.

These phenomena are worsened when the metal part is rigid, and thusthick, or when at least one dimension of the area of contact issubstantial, which makes it necessary to reinforce the bond byadditional mechanical means such as screwing, rivetting, seaming, etc.

A second problem is therefore to effect a very strong bond between theparts of the component made of an organic matrix composite and the partsmade of metal, metal alloy or ceramic.

The low resistance of organic resin to abrasion and to impact fromforeign bodies poses problems particularly in the case of aircraftpropellers. These same problems also arise with the blades of turbineengines for aircraft, especially the fan blades which are situated wellto the front of the engines. Indeed, as such blades rotate at speeds ofup to 3000 rpm, and may have a height (from root to tip) of up to 1200mm with a thickness below 30 mm, they are particularly exposed toabrasion by sand entering the engine, or to impact from heavy foreignbodies such as birds.

To overcome these problems, the leading edge of the blade may be coveredby a metal coating, but there is then the bonding problem referred topreviously. German Patent 4411670 describes a blade in which the bondingof its leading edge to the remainder of the blade is reinforced byscrews and seams.

This solution requires additional manufacturing operations, and thestrength it achieves remains limited since an excessive number of seamswill weaken the blade by the multiplication of the holes made throughit. The leading edge is therefore thin and flexible, which does notallow it to withstand properly impacts from heavy objects such as birds.

The low resistance of organic matrix composite materials to localizedcompressions, for example of punching type, originates from the factthat reinforcement fibres have no effect under this type of stress,whereas they are very effective with respect to tensile stresses. Thisproblem arises in the provision of fixing points for rivets or bolts incomponents made of composite material, for example, air intake casings,covers or cones for aircraft engines. The problem is only partly solvedby using rivets or bolts with wide heads and nuts, as such width remainslimited, and substantial concentrations of stresses subsist at thefixing points, requiring a reduced tightening force and an increase ofthe number of fixing points.

U.S. Pat. No. 4,006,999 discloses a turbomachine blade made of acomposite fibre-resin material and including a metal leading edge widelycovering the convex and concave flanks of the blade. The composite partof the blade is itself composed of two parts holding grids in thevicinity of the mean plane of the blade. These grids protrude forwardand are embedded in the metal constituting the leading edge, so as tostrengthen the bond between the leading edge and the remainder of thecomposite blade. However, the effectiveness of such a solution remainslimited, as this bond is effected essentially at the centre of theleading edge, the bonding of the flanks of the leading edge with theremainder of the composite blade being achieved only by adherence.Furthermore, the method of making and assembling the leading edge withthe remainder of the blade is not clearly apparent.

The low temperature resistance of organic resins restricts theutilization of components made of composite materials incorporating suchresins. A process is known for the thermal protection of metal parts inwhich plasma projection is used to produce a heat insulating ceramicshield on the surface of the parts. However, the application of thisprocess to parts made of composite material having an organic matrixgives rise to two difficulties:

Firstly, it is not applicable to parts of substantial dimensions becauseof the great difference between ambient temperature and the temperatureat which molten ceramic sets, and of the vitreous type of fracture ofthe ceramic.

Indeed, on cooling, the ceramic, because it has a greater thermalexpansion coefficient, will contract more rapidly with a high risk ofcracking, a high compression of the composite material part, and asubstantial concentration of stresses tending to bring about detachmentof the ceramic layer.

Secondly, the heat released by the plasma projection of molten ceramiconto the part made of composite material will cause considerabledegradation of the resin, reducing the strength of the part. Thereleased heat will also bring about the destruction by pyrolysis of theresin in the vicinity of the surface of the part, which reduces thestrength of the bond between the ceramic layer and the composite part ofthe component.

A process is known for the protection of components made of a compositematerial consisting of reinforcement fibres and organic resin, involvingplasma projection of a layer of molten metal or metal alloy onto thecomponent. This process suffers from the drawbacks described above, andalthough the danger of cracking may be reduced by using a malleablematerial, the process is restricted to the formation of thin protectivecoatings on components which are not greatly stressed.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a hybrid high strengthcomponent comprising a first part, termed the soft part, made of acomposite material consisting of a fibre-reinforced organic resinmatrix, and at least one second part, termed the hard part, made of amaterial selected from the group consisting of metals, metal alloys andceramics, said second part being able to have large dimensions and tohave at least one place where its dimension in any direction is at least8 mm, and said component having a very strong bond between the firstpart and the second part.

To this end the invention proposes to provide the component with atransition layer between said soft part and said hard part andcompletely separating said soft part from said hard part, the saidtransition layer being made of a composite material comprising a matrixwhich is weldable to the material of said hard part and reinforcementfibres embedded in said matrix, said reinforcement fibres being formedby extensions of said fibres of said soft part whereby saidfibres/reinforcement fibres intersect the boundary between the said softpart and said transition layer at least at the periphery of saidboundary.

In this way a particularly strong bond is obtained thanks to a doublecontinuity, namely continuity of the matrix of the transition layer withthe material of the hard part, and continuity of the reinforcementfibres of the transition layer with those of the soft part.

It will be appreciated that this double continuity, at least at theperiphery of the transition layer, achieves a high shear strength of thehard part on the soft part, this shear strength being even moreappreciable when the hard part forms a projection from the soft part.

The bonding is even better when the double continuity extends throughoutthe surface of the transition layer.

The thickness of the transition layer and the depth of penetration ofthe fibres of the soft part into the transition layer are not critical.It will be sufficient for the fibres to be fully embedded in the matrixof the transition layer and the matrix of the soft part of thecomponent, such that said fibres are held by the said matrices. Thismakes it possible to eliminate the cause of decohesion of the soft partwith the hard part by rupture of the matrices, and by decohesion betweenfibre and matrix in the vicinity of the boundary separating thetransition layer from the soft part.

Preferably, the matrix of the soft part and the matrix of the transitionlayer will make mutual contact in order to ensure the fibres areembedded in the vicinity of the boundary between the soft part and thetransition layer, thereby ensuring that the bond is not weakened in thishighly stressed area.

Preferably the fibres pass through the boundary between the soft partand the transition layer at an angle of between 15° and 75° to the saidboundary, so as to increase the capacity of the fibres to resist thedetachment of the soft part from the transition layer.

In a preferred embodiment, the reinforcement fibres each form an elbowin the transition layer and extend on both sides of the elbow into thesoft part. This helps to improve the gripping of the fibres by thematrix of the transition layer, to reduce the thickness of the saidtransition layer, and to increase the strength of the bond between thesoft part and the transition layer.

Preferably the reinforcement fibres will belong to sheets of fabricoccupying the volume of the soft part at least in the vicinity of thetransition layer, the sheets of fabric extending into and occupying thevolume of the transition layer. The effect of this is to achieve thepassage of a high number of fibres through the boundary between thetransition layer and the soft part, these fibres being well distributedover the area of the boundary and intersecting in this region as weftthreads and warp threads, thereby reinforcing the bond between the softpart and the hard part of the component. Such a structure also verysimply enables the fibres to be disposed all over the boundaryseparating the transition layer from the soft part, thus increasing thestrength of the bond between the hard part and the soft part.

The sheets of fabric may belong to a mono-fabric, so as to increase thenumber of fibres passing through the boundary between the transitionlayer and the soft part and thereby strengthen still further the bondbetween the soft part and the hard part of the component.

The invention should not be confused with the component disclosed in theabove-mentioned U.S. Pat. No. 4,006,999. In the present invention, thetransition layer completely separates the hard part from the soft part,the reinforcement fibres passing, at least at the periphery, through theboundary between the transition layer and the soft part and beingenclosed by the matrices of the transition layer and the soft part,thereby forming a strong bond between the hard part and the soft part.In U.S. Pat. No. 4,006,999, the transition layer corresponding to thatof the present invention is localized at the centre of the hard part,and the fibres that extend away from it are simply tangential to thehard part and to the soft part. This arrangement therefore does notenable a bond to be obtained between the hard part and the soft partwhich is comparable to the bond obtained with the present invention.

The invention also provides a method of manufacturing such componentsimplementing the well known RTM (resin transfer moulding) process, themethod including the following steps:

a) making a fibre preform to the shape of the soft part of the componenttogether with the transition layer;

b) forming the transition layer by plasma projection of a moltenmaterial onto a portion of the preform, said material being weldablewith the material of the hard part;

c) forming the hard part of the component, particularly in rough form,on the transition layer;

d) inserting the assembly constituted by the preform, the transitionlayer and the hard part into a mould; and

e) injecting resin into the mould so as to impregnate the preform toform the soft part, polymerizing said resin, and removing the resultingassembly from the mould.

Depending on the shape to be obtained, the formation of the hard partmay be effected by:

f) building up the material of the hard part using flame, electric arcor plasma projection; or

g) machining the second part, and welding it to the transition layer.

After polymerization of the resin, and removal of the assembly from themould, the hard part will generally be the subject of a complementarymachining and finishing operation.

Preferably the mould will have a cavity which surrounds the hard partwith enough clearance for there to be no contact between the walls ofthe mould and the hard part.

Before the injection of resin, the space left free between the hard partand the walls of the mould will be filled with an elastomer. This hastwo advantages:

elimination of the risk of deformation of the component as a result of awall of the mould pushing against the hard part, which is still notprecisely shaped at this stage of the process; and,

saving on resin, as the elastomer prevents the very liquid resin frommoulding around the hard part.

In a particular embodiment of the invention, the hybrid component is aturbomachine blade, such as a fan blade for an aero-engine, the bladecomprising an aerodynamic portion made of a composite material having anorganic matrix, and a metal alloy leading edge added to it.

Preferably, the blade will be formed with a fibre preform constituted bya stack of sheets of fabric arranged parallel to the mean plane of theaerodynamic portion of the blade, the upstream edge of each sheetreaching as far as and extending into the transition layer. The frontedges of the sheets will preferably form a bulge or bulb extending intothe leading edge, so as to increase the area of the transition layer,and, in consequence, the solidity of the bond between the soft firstpart of the component and the transition layer.

Also, the fibre preform will preferably be in the form of a monofabric,the warp threads joining the sheets together forming elbows in thetransition layer, and improving the gripping of the fibres by the matrixof the transition layer.

In the case of a fan blade for an aircraft engine, the fibre is usuallymade of high-strength carbon, silicon carbide (SiC), or some othermaterial with equivalent properties, and the leading edge will be madeof a titanium alloy TA6V. With a thickness of from 8 to 10 mm, measuredin a direction proceeding downstream of the blade, the leading edge willhave a much improved rigidity compared to the leading edge of theabove-mentioned German Patent 4,411,679. This rigidity can be improvedwithout trouble by raising this thickness to at least 20 mm, which willmake the blade particularly resistant to impact from heavy foreignbodies, in spite of its great lightness relative to blades made entirelyof metal.

In another embodiment of the invention, the soft first part is a wall,for example of a casing, a cover or an air intake cone, and the hardsecond part is a boss or a plurality of bosses formed on the said wall.

In yet another embodiment of the invention, the hard second part is aceramic heat shield applied, for example, on the inner wall of aturbomachine casing.

The present invention should not be classed as being a new use of thesurface treatment process involving plasma projection of molten metal ormetal alloy on a part made of composite material having an organicmatrix, or any alternative of this process, nor as articles thusobtained. In contrast:

a) the metal or ceramic part is not a simple coating but a prominentpart of variable shape, and is welded to the matrix of the transitionlayer which is interpenetrated by the fibres of the first part;

b) this metal or ceramic part is obtained by building it up withmaterial, or by welding a formed part, prior to the resin impregnationof the fibre preform.

As a result hybrid components are obtained in which the metal or ceramicportion may protrude substantially from the composite portion having anorganic matrix, and which possess:

a very strong bond of the welded type between the two portions; and,

perfect soundness of the material of the portion made of organiccomposite material.

The invention is particularly useful in the case of large-sizedcomponents as, during the cooling of the hard second part, the fibres ofthe first part, which are not immobilized by the resin matrix, followthe contractions of the second part without internal stress. Thesubsequent polymerization of the resin will then produce only lowinternal stresses, as it is carried out at a temperature ranging from100° C. to 300° C., i.e. very much below the fusion temperature of theceramic or metallic second part, which is from 1300° C. to 1700° C. Forthe same reasons, the invention enables components to be made withlarge-size ceramic parts without the risk of cracking caused by thevitreous rupture of the ceramic during cooling.

The present invention is not restricted to components having a singlesecond part, and the term "second part" is intended to denote one ormore separate parts. It may be the case, for example, that a blade maybe reinforced by a metal or metal alloy addition not only at the leadingedge as described earlier, but also on the flanks of the root by whichthe blade is held, and at the trailing edge. This may also be the casefor a casing or a cover having a plurality of bosses.

The invention will now be further described with reference to thepreferred embodiments, given by way of example only, and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a bar made of a composite material having an organic matrixand to which a metal end has been joined in accordance with theinvention.

FIG. 2 illustrates the structure of a monofabric in the transition layerand in the vicinity of the latter in a component of the invention.

FIG. 3 illustrates the moulding of the bar shown in FIG. 1.

FIG. 4 illustrates the bar when the metal end part is machinedseparately and welded to the transition layer.

FIG. 5 illustrates the forward part of a blade constructed in accordancewith the invention.

FIG. 6 illustrates the fashioning of the leading edge of the blade byplasma projection.

FIG. 7 illustrates the moulding of the blade.

FIG. 8 illustrates a wall of organic composite material having a bossformed on it according to the invention.

FIG. 9 illustrates the fashioning of the boss on the wall.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The component shown in FIG. 1 is a bar comprising a body part 1 and anend part 2 separated by a transition layer 3. 4 and 5 denote theboundary surfaces between the transition layer 3 and the parts 1 and 2respectively.

The part 2 has at least one place where a dimension d in any directionis at least 8 mm, and may project from the part 1. In other words animaginary sphere of diameter d may be inscribed in the part 2.

The part 1 is composed of high-strength fibres 6a capable ofwithstanding high temperatures, such as fibres of carbon, siliconcarbide (SiC) or boron carbide, the fibres 6a being embedded in a matrix7 of organic resin hardened by polymerization.

The transition layer 3 is composed of fibres 6b which are extensions offibres 6a, the fibres 6b themselves being embedded in a matrix 8 of amaterial which is weldable with that of the part 2. The material of thepart 2 may be metal, a metal alloy or ceramic.

Denoted by 6 are the fibres which have a segment 6a in the part 1 and asegment 6b in the part 2. In order that the fibres 6 are held tightly inthe vicinity of the boundary surface 4, the matrix 7 of the part 1reaches as far as contact with the matrix 8 of the transition layer 3.This prevents the fibres 6 from being in overhanging position, andimproves the bonding between the part 1 and the transition layer 3. Thebond between the transition layer 3 and the part 1 may be improved asregards shear stress by arranging that the fibres 6 pass through theboundary surface 4 at an angle of incidence of between 15° and 75°relative to the surface 4.

With reference now to FIG. 2, the fibres 6 are shown included in amonofabric, that is to say in a fabric made up of several layers of weftthreads 10 connected together by the threads 6. These threads 6, as theypass around the weft threads 10 at the surface of the fabric, formelbows 6b within the transition layer 3, while the portions 6a of thethreads leading from the elbows 6b extend into the monofabric within thepart 1. With such an arrangement, the threads 6 perform an effectivehooking between the transition layer 3 and the part 1, and hencereinforce the bond between the said transition layer 3 and the part 1.

A first embodiment of the method of making a component in accordancewith the invention is illustrated in FIG. 3, and comprises the followingstages.

a) Making a fibre preform 11 to the shape of the part 1 increased by thetransition layer 3. Such preforms are known to the specialist and mayconsist of sheets of fabric assembled as a monofabric and/or simplywoven threads or strips wound on a core.

b) Making the transition layer 3 by plasma projection of molten materialwhich is the same as that used for the part 2 or is weldable with thematerial of the part 2, which could be a metal, a metal alloy orceramic. Masks, not shown, may be placed against the preform 11 right upto the line of the boundary 4 which is to be formed so as not to projectmolten material on the remainder of the preform 11.

c) Making a rough form 2a of the part 2 with sufficient over-thicknesson the transition layer, by depositing the material of part 2 dropwisein molten form by flame or electric arc deposition.

d) Placing the unit thus obtained, i.e. consisting of the preform 11,the transition layer 3 and the roughly formed part 2a, in a mould 14including walls 15 defining the shape of the part 1 and a cavity 16surrounding the rough part 2a with adequate clearance, taking intoaccount the unevennesses of the rough part 2a.

e) Injecting an elastomer between the walls 17 of the cavity 16 and therough part 2a to fill up the empty space therebetween.

f) Injecting liquid resin by the RTM (resin transfer moulding) processinto the preform 11 bounded by the walls 15, to produce the part 1.

g) Demoulding the unit and machining the rough part 2a to make thefinished part 2.

FIG. 4 illustrates a variant of the embodiment just described. In thisvariant the unit consisting of the preform 11 and the transition layer 3is produced in conformity with the above steps (a) and (b).

The surface 5a of the transition layer 3 is machined, and apre-machining of the part 2, is effected, including providing the partwith a surface 5b with a shape complementary to that of the surface 5a.

The part 2 is then welded to the transition layer 3 by brazing togetherthe surfaces 5a and 5b. The component is then finished in accordancewith the above described steps (d), (e), (f) and (g).

FIG. 5 shows an embodiment of the invention in the form of aturbomachine fan blade including a first part 1 which constitutes theblade proper, a second part 2 which constitutes the leading edge, and atransition layer 3 between the parts 1 and 2.

The blade proper (i.e. the aerodynamic portion) is made of a compositematerial including a matrix 7 of organic resin reinforced withhigh-strength carbon fibres 6. The blade has a concave flank 20 orintrados face, and a convex flank 21 or extrados face. 20a and 20brespectively denote the portions of the intrados face 20 on the part 1and the leading edge part 2, and 20c denotes the line of demarcationbetween the portions 20a and 20b. 21a and 21b respectively denote theportions of the extrados face 21 on the part 1 and the leading edge part2, and 21c denotes the line of demarcation between the parts 21a and21b. Also, 22 denotes the imaginary mean plane half way between theintrados face 20 and the extrados face 21, which two faces meet in themean plane 22 to define the foremost line 23 of the leading edge 2. Thelines 20c and 21c define the rearmost lines of the leading edge 2.

The part 1 has a projection 24 which penetrates widely into leading edge2. This arrangement increases the area 4 of the transition layer andthus improves the bonding of the parts 1 and 2, particularly againstshear in response to stress applied perpendicularly to the mean plane22. The forward end of the projection 24 is denoted at 25.

In its bulkiest part, that is to say just in front of the projection 24,the leading edge 2 has a dimension d in any direction of at least 8 mm.In other words, a sphere of diameter d=8 mm can be inscribed within theleading edge 2.

Preferably, this leading edge 2 will have a dimension 1 along the meanplane 22, i.e. between the lines 23 and 25, at least equal to thethickness e of the blade in order to improve the rigidity of the saidleading edge 2.

Preferably, the reinforcement fibres 6 will belong to sheets of fabricarranged parallel to the mean plane 22. This arrangement is economic toachieve, and allows a maximum number of fibres 6b to extend into thetransition layer 3 for a strong bonding of the transition layer 3 to thepart 1.

This is an advantage of the invention over the prior art. Due to thefact that the edges of the sheets 26 of fabric flush with the surface ofthe blade are very vulnerable to impacts from foreign bodies, it isusual to arrange these sheets 26 parallel to the intrados and extradosfaces 20 and 21 so as to bring the edges of the sheets to the inside orto the rear of the blade. In the present invention, on the other hand,the leading edge 2, which is very rigid against front to back stressesand widely surrounds the front of the part 1, efficiently protects theedges of the sheets 26.

The use of a monofabric in this second embodiment has the advantagesalready described with reference to the first embodiment.

Referring now to FIG. 6, the blade is produced as follows. A fibrepreform 11 is made to the shape of the part 1 of the blade, includingthe projection 24 and the transition layer 3, using sheets of fabric 26parallel to the mean plane 22. These fabric sheets can be cut outseparately to the required shape, stacked, and then sewn together.Preferably they will form an integral part of a monofabric. Thetransition layer 3 is then produced by plasma projection of material onto the portion 24 as far as the lines 20c and 21c. A rough formation 2aof the leading edge 2 is then built up by adding material. In apreferred embodiment, this material is deposited with a plasma torch 28projecting a conical beam 29 of droplets of the molten material on tothe transition layer 3. The torch 28 is shifted in the plane of FIG. 6along a trajectory 30 initially enveloping the projection 24, and movingaway progressively from the projection 24 in the direction 31 towardsthe front of the leading edge 2, as the rough formation 2a grows.Reference 30a indicates the front of the trajectory 30, i.e. theintersection of the said trajectory 30 with the mean plane 22 at thefront of the blade.

This trajectory 30 is combined with a trajectory along the leading edge2, i.e. in a direction perpendicular to the plane of FIG. 6.

In the preferred embodiment, the operation will start with the torch 28depositing a strip of material on the projection 24 along the line 20cor 21c following a trajectory perpendicular to the plane of FIG. 6. Thetorch 28 will be displaced along the trajectory 30 towards the point 30ato deposit another strip of material adjacent to the first with apartial overlap, and so on until the other end 21c or 20c of the roughformation 2a is reached. Similarly, successive layers of material willbe deposited by progressively staggering the trajectory 30 in thedirection 31, the path of the torch 28 becoming increasingly shorter onboth sides of the point 30a, and the torch finally becoming immobilizedat the point 30a to deposit the last strips of material along the line23.

In order that the material deposited has a variable thickness: thin inthe vicinity of the lines 20c and 21c, and thick towards the line 25,the plasma torch 28 will be slanted by an angle β so as to direct theflow of material 29 towards the rear of the blade. This ensures thatless material is deposited in the part 29a of the flow 29 toward therear of the blade, and more material is deposited in the part 29b of theflow toward the front of the blade. Thus, in a single pass, the strip ofmaterial deposited is thick along one edge and thins down towards theother edge. The shaping of the rough formation 2a is carried out using astandard digitally-controlled six-axis machine. Perfecting the processin each different case according to the shape to be obtained is withinthe normal experimental capabilities of the specialist.

With reference now to FIG. 7, the sequence of operations followed inmaking the component is similar to that of the preceding embodiment. Theunit consisting of the preform 11 and the rough formation 2a is placedin a mould 14 having walls 15 which define the shape of the finishedpart 1, and a cavity 16 which surrounds the rough formation 2a withadequate clearance, the boundary between this cavity 16 and the walls 15facing the lines 20c and 21c. The space left between the rough formation2a and the walls 17 of the cavity 16 is filled by injection of anelastomer. The part 1 is then shaped by injection and polymerization ofresin by the RTM process. The blade is then removed from the mould, andthe final leading edge 2 is machined from the rough formation 2a.

The plasma torch 28 is the preferred means of producing rapidly theaerodynamic profile of the leading edge 2 of the blade, particularlywhen the dimensions of the blade are great. Deposition of material byflame or electric arc, as well as the welding of a separately machinedpart, may also be effected, especially when the dimensions of the bladeare small.

In the embodiment shown in FIG. 8, the part 2 is a boss on the wall 1 ofa casing or a cover, the reinforcement fibres of which are provided bysheets of fabric parallel to the wall. The boss 2 projects from the wall1 and is fastened to this wall 1 by the transition layer 3 having anarea substantially identical to that of the base of the boss 2. Thisboss 2 has an overall circular shape about an axis 35, a machinedsurface 36, which is plane and parallel to the wall 1, and a machinedhole 37 on the axis 35 passing through the boss 2 and the wall 1.

As shown in FIG. 9, after the preform 11 of the wall 1 has beenproduced, a plasma torch 28 is set up on the axis 35 of the boss to bemade, and the operator fashions in succession the transition layer 3 andthe rough formation 2a of the boss 2 by the projection of a conical flowof droplets of molten material on to the preform 11. Several projectionsare effected, in each case the torch 28 being moved away from the wallof the preform 11 in the direction 31 parallel to the geometric axis 35so as to superimpose ever wider layers 38 of the material and thusproduce the roughly shaped boss 2a.

In the case of bosses of extensive shape, the movement 31 of the torchis combined with an orbital movement parallel to the wall 1.

The component is then fashioned as in the preceding examples.

Generally, in the case of large components, it will be antageous to makethe preform 11 with fibres 6 coated with a very thin layer of resin andto insert the preform into the mould 14 for polymerization to its finalshape as a preliminary step. This sufficiently stiffens the preform 11to facilitate the forming of the transition layer 3 and the roughformation 2a while retaining the advantages of the dry preformpreviously described.

We claim:
 1. A method of manufacturing a hybrid component with a highstrength/mass ratio, said component comprising a first part, termed thesoft part, made of a composite material consisting of fibers embedded inan organic resin matrix and at least one second part, termed the hardpart, made of a material selected from the group consisting of metal,metallic alloys and ceramics, said method comprising the steps of:makinga preform of fibers for said soft part; using a plasma torch to projecta material in molten form on to a portion of said preform to form atransition layer for the attachment of said hard part, said materialbeing weldable to the material of said hard part; depositing thematerial of said hard part in molten form on said transition layer toroughly fashion said hard part into a rough formed hard part;introducing an assembly constituted by said preform, said transitionlayer and said rough formed hard part into a mold; injecting resin intosaid mold so as to impregnate and embed said preform to form said softpart, polymerizing said resin; removing the resulting assembly from saidmold; and machining said rough formed hard part to finish said hardpart.
 2. A method according to claim 1, wherein said mold includes acavity surrounding said rough formed hard part and said method furthercomprising the step of injecting an elastomer into said cavity to fill aspace between said rough formed hard part and a plurality of walls ofsaid cavity thereby forming an elastomer coating so as to prevent entryof said resin into a volume occupied by said elastomer coating of saidmold.
 3. A method according to claim 1, wherein the preform isconstituted by sheets of fabric whereby at least one edge of said sheetsis exposed at a surface facing said hard part so as to reinforce a bondbetween said transition layer and said soft part.
 4. A method accordingto claim 1, wherein the preform is constituted by a monofabric, whereina plurality of warp threads of said monofabric are exposed at a surfacefacing said hard part so as to form elbows in said transition layer. 5.A method according to claim 1, wherein the preform is made from fiberscoated with a thin layer of resin, wherein said method further comprisesthe step of preliminarily polymerizing said preform to its final shapeto stiffen it before said transition layer is produced.